This invention relates to a switching type power supply of the type employing alternately conductive switching elements.
Switching type power supplies are well known in the art, and generally employ a transformer having a primary winding provided with an alternating current by two or more switching transistors, and a secondary winding coupled to rectifying and filtering means for delivering one or more DC voltages to a corresponding load or loads.
When such power supplies are operated at high power levels, it is essential to insure that the alternately conductive switching transistors never are both "on" at the same time, a condition which would cause the destruction of said transistors. While circuits are presently available for assuring such non-coincidence, such as the "Switch Mode Regulator Control Circuit" sold by Motorola Semi-Conductors, Phoenix, Ariz. as integrated circuit Nos. MC 3420 and MC 3520, these circuits are relatively complex and there is need for a relatively simple and inexpensive control circuit for this purpose.
There is also need for circuitry to sense an overload condition of the switching transistors as rapidly as possible, so that feedback and control of the drive voltage to said transistors can be modified in sufficient time to prevent destruction of the switching transistors.
In a switching type power supply of the aforementioned type having a plurality of secondary output voltages, there is need for a relatively simple regulator which is capable of regulating a given one of said secondary voltages without adversely affecting the other secondary voltages.
In order to provide improved efficiency and an additional margin of safety, it is desirable that the circuitry which provides the driving signal voltages to the switching transistors be supplied with power from the secondary winding of the transformer, so that a short circuit condition at the load or loads will immediately result in a loss of drive to the switching transistors to disable the same thus protecting the supply from damage in the event of such a short circuit condition at the load.
Accordingly, an object of the present invention is to provide a switching type power supply having one or more of the aforementioned features.